So let's take a look at some of the things that actually changed for us, especially those that have been gone since whenever ago and have no idea what the heck just happened.

Originally Posted by MMO-Champion

First off, NEW TALENT TREE. And it's class wide. You get 1 every 15 levels, and can only spend it on one of the three choices of that tier. They can, however, be changed on a fight-per-fight basis, using a consumable similar to Dust of Disappearance for Glyphs. I've got them listed here:

Shadowfiend - Is now a 3 minute cooldown (down from 5 minutes). The cooldown of this spell is no longer affected by Mind Flay critical hits.

Shadow Word: Death no longer does damage to yourself baseline but only castable on low health targets (redacted with a glyph). Its original cooldown reset glyph is incorporated into the spell baseline.

Discipline

Archangel is now Discipline exclusive. It now increases healing by 5% per stack (up from 3%), but no longer restores mana.

Atonement can trigger from offensive use of Penance, but does not stack Grace while doing so.

Inner Focus now reduces mana cost by 25% (down from 100%) and increases crit chance by 100% (up from 25%)

Rapture is now based off 150% of your spirit's value on triggering, rather than max mana.

Holy Word: Sanctuary now acts as a Heal over Time, gaining additional ticks from haste rating, but no longer triggering Echo of Light (mastery). It once again correctly diminishes in value on more than 6 targets.

Chakra: Serenity now increases all affected heals by 15%, rather than their crit chance.

Renew is now treated as a Single Target heal for the purpose of increased output

Inner Focus - When you cast Inner Focus you become immune to Silence, Interrupt, and Dispel effects for 5 sec.

Inner Sanctum - Spell damage taken is reduced by 6% while within Inner Fire, and the movement speed bonus of your Inner Will is increased by 6%.

Mind Blast - When you critically hit with your Mind Blast, you cause the target to be unable to move for 4 sec.

Mind Spike - When you deal damage with Mind Spike, the cast time of your next Mind Blast is reduced by 50% lasting 6 sec. This effect can stack up to 2 times.

Reflective Shield - Causes 45% of the damage you absorb with Power Word: Shield to reflect back at the attacker. This damage causes no threat.

Shadow Word: Death - Your Shadow Word: Death can now be cast at any time, but deals 25% damage against targets above 20% health and does not generate a Shadow Orb when used against them. Casting Shadow Word: Death now also does damage to you equivalent to the damage it would do to an enemy above 20% health.

New Glyphs:

Dark Binding - You can now cast Prayer of Mending, Renew, and Leap of Faith without cancelling Shadowform.

Retaining Rapture will give Disc an unfair advantage in the mana department over Holy. However, since it is now based off of Spirit, Disc will have nearly as bad regen as Holy.

Spirit Shell is a very nice cooldown to have. I'm glad they didn't stick with the old version.

Archangel/Atonement no longer cost talent points. Are they truly optional? Blizzard is riding the razor's edge with this for people who don't like to DPS while healing. It is very difficult to balance. If I wanted to DPS I'd roll a DPS. Personally I think they need to take away AA or give Discipline another way to generate Evangelism stacks besides DPSing. Then Atonement becomes more of an option rather than a requirement like it nearly is now.

Discipline is starting to feel like my Warlock on live: running out of keybinds...

Holy

Holy's mana continues to be terrible.
Chakra is still terrible.

Lightspring is the best thing to happen to the spec in beta. Thank you, Blizzard, I no longer have to yell at my raid to click.

The loss of Divine Hymn from Disc is actually a buff to Holy. Hooray buffs!

A stronger Renew makes a pretty strong argument for going Inner Will, Chakra: Serenity, and Renew spam, and swapping to Chakra: Sanctuary and Inner Fire for AOE burst phases. That playstyle may not be viable in 25s, but Holy's issues aren't as glaring in 25s. The mana will still be an issue.

Overall, Holy is still a jumbled mess, mostly thanks to Chakra. Mana is a big issue. Lightspring and a strong Renew are steps in the right direction, but the spec has a long way to go. I am going to reroll Monk and come back in an expansion to see how things are going.

Shadow

The nerf to multidotting will be the biggest change from live. Yes, we'll still be able to DOT multiple targets, and our damage will increase, but it won't be anything to write home about, and it may turn out not to be worth it in a lot of situations. Still waiting for the compensating single-target damage buff.

Removing Evangelism and Empowered Shadows: personally, I liked watching buffs on myself, but I can see this as a net win because of the removal of ramp up in our rotation.

Mind Blast generating orbs feels too much like the combo point system. Devouring Plague as a finisher feels pretty "ho hum" as well.

Vampiric Embrace will be nice utility. Void Shift will be nice utility for all specs, Shadow will be able to Disperse afterwards, which is a nice perk.

The new mastery is pretty boring.

They took away Dark Archangel. WAAAAAH!!!! Putting wings on Devouring Plague through a glyph just isn't the same, and neither is PI.

Overall: right now, it all depends on how the numbers pan out for shadow. If the multidotting nerf is too big, it effectively removes that ability from the class. If our single target damage is still low, our general viability comes into question.

Talents

Level 15 tier: Hopefully, this tier will actually make Shadow competitive against melee in PVP. Not holding my breath, though.
Level 30 tier: I'm excited to have Body and Soul for all specs in PVE, and Phantasm in PVP
Level 45 tier:

Power Word: Solace - they need to nerf or remove this, or buff FDCL and Mindbender for the other specs. It is becoming too much of a prop for our mana and we have to spend GCDs that other healers don't, again, just to prop up our mana into something resembling the passive regen/efficiency of other specs.

Shadow Word: Insanity - I'm not even sure what the point of this is, other than something to replace Solace for Shadow. A replacement for the lost burst from guaranteed MB crits while Mind Spiking?

Level 60 tier: Desperate Prayer for all specs is great. Spectral Guise I don't see too much use for, even in PVP. Angelic Bulwark - situationally useful.

Level 75 tier: PI as Shadow will be nice. I'd still rather have Dark Archangel, I felt it fit the spec much better thematically.
Level 90 tier: Halo looks pretty cool. Otherwise, eh, more damage and healing buttons to push, pretty unremarkable. Positioning could be really annoying with these.

Glyphs

Being able to cast heals while in Shadowform will be amazing for PVP.
Lightspring - still amazing.
Mind Spike - not sure why they removed the auto crit when you spend this buff on MB. Only 2 casts instead of 3 could have interesting effects.
Spirit of Redemption - why do we still have this ability? Oh yeah, so other players can laugh at us in PVP!
Holy Nova - why do we still have this ability? Oh, yeah, killing snake traps in PVP!

Overall, I'm happy I don't have to choose between DPS and non DPS glyphs anymore. I can slot Dispersion again, yay! There are some interesting choices too - like Renew and PW:S glyphs, where it could go either way.

Discipline
Rupture - from spirit for the first time ever makes me uneasy, would have liked it better reverted to as it was in Wrath, by Spellpower.
Loss of Divine Hymn - A situational tool lost for nothing to take its place(SS is new but doesn't cover the spread out targets).
Holy Nova - Stays in form of a MAJOR glyph. Not going to be worth it as it is still weak since the transition from Wrath when it was ~ok'ish.
PW-Solace - I hate this one so much... If they make me use it to beat a boss I will dislike them all!
Spirit Shell - Thankfully it turned out ok in the end, but all this grp-based AoE healing still goes on with PoH.
Smitespec - Not a choice anymore. Balance us around that and force us to PW:Solace too and we're set for a bad time^2

What I wish for: Multitarget Penance - triggered by Inner Focus. Would be more powerful then CoH but with a way longer cd(~Current target + 3 lowest). Just that missing tool for the job, we're priests aren't we?

If I was going to play MoP, I'd almost definitely be rerolling to my Paladin with the state of things right now. The fact you literally have to sit and spam PW: Solace for 40-50% of a fight to sustain your mana is an absolute joke, which Blizzard keep avoiding. Throughput would be decent if you didn't have to sit there regaining mana all the time.

Listen to this man since he speaks the truth, disc as it stands now is completely useless unless you plan to tank heal or need the cds it provides, holy is leagues above it in pretty much everything else.

Listen to this man since he speaks the truth, disc as it stands now is completely useless unless you plan to tank heal or need the cds it provides, holy is leagues above it in pretty much everything else.

Has anyone tested how does FDCL work with glyph of Mind Spike, both single and multi target?
Having instant or 50% reduced cast time on Mind Blast sounds interesting. No idea if any of the new raid bosses have a mechanic where this could be handy since I don't have beta access.

I ran a couple of MoP heroics with my disc priest and then with my resto druid. I had a far easier time keeping the group alive and managing mana with the druid, despite being much more practiced with disc on live. Its anecdotal, but disc definitely left a sour taste in my mouth...

Just because you can't keep up doesn't mean the entire spec sucks. I'm doing just fine with it. While mana is tedious, it has still been tons of fun.

The CLASS sucks. You can't run with weaker players (And/or specs) and top the meters and say everything is cool. It doesn't work like that. There's some serious issues with mana and mechanics and it's not getting better.

Holy may be the best of the bunch, but Disc and Shadow are absolute garbage and Holy's got problems too.

Been playing disc since the end of TBC and I've never felt so broken before.

Sad to see myself at the bottom of healing meters. If my only aim would be to top meters, which I can do, I'd go oom fast even after popping mana CDs while the rest of the healers (maybe except for shamans) are sitting on 50+% more mana.

Finding myself a bit overwhelmed with the number of keybinds now, let alone the management of so many cooldown and being careful not to let evangelism stacks fall off. Everything just feels so out of sync. I'm hoping that maybe once I get more accustomed to the encounters I'd be able to time cooldowns appropriately.

So far on beta I see disc performing better in 10s than in 25s, based on my personal experience.

This doesn't look like balanced to me. There may be mitigating factors (Monks look like they're still broken), but the more logs I see, the more I see Priests riding the bottom.

If you see that as getting handled then that's a differing of opinion. Monks SCK was healing for too much (no DR) and Paladins have a bug with the Eternal Flame glyph or something.

I've been progression raiding since vanilla - you'll never be equal - but it sure is fine to keep up. Did you look at ALL of the logs? Or just that fight and those attempts? I'm talking about OVERALL not just one fight or one attempt.